Photoresist (also known as photo-resist) refers to an etching resist film material whose solubility will change when it is irradiated or radiated by a light source such as a ultraviolet light, an excimer laser, electron beam, ion beam and x-rays. Photoresist is mainly used in microfabrication of integrated circuits and semiconductor discrete devices and finds a wide range of applications in manufacturing panel displays, LEDs, magnetic heads and precision sensors. The photoresist may be applied onto semiconductors, conductors and insulators by means of its photochemical reaction, due to photochemical sensitivity of the photoresist, and the remained portion after exposure and development provides protection for the substrate. Then a required fine pattern may be transferred from the mask onto the substrate to be processed by etching with the etchant. Therefore, the photoresist is a key material for the microfabrication technology. With improvements of technical requirements for integrated circuits, the resolution of a photolithography technology needs to be improved accordingly, from the early G-line (436 nm) photolithography, I-line (365 nm) photolithography, deep UV (248 nm) photolithography to the current 193 nm photolithography and further to the most promising next generation extreme ultraviolet (EUV, 13.5 nm) photolithography, and the photolithography technology accordingly put greater demands on the photoresist.
The main material of existing photoresist used in the 193 nm photolithography usually employs a low molecular weight polymer with the molecular weight of 5,000-15,000 Daltons. Such polymeric material may affect the edge roughness or line width roughness of the pattern generally due to the factors such as too large molecular volume, dispersive molecular weight and molecular chains' intertwinement, so that such polymeric material does not meet the demand of a fine photolithography. Therefore, it is very important to develop a novel photoresist for the photolithography technology.
Molecular glass is a kind of small molecule compound having specific structures and functions, which is proposed and developed in recent years. Such small molecule compound has an exact molecular structure, monodispersity and a small radius of gyration, meanwhile possesses thermal stability and film-forming property of a polymer, therefore it is expected to become a new kind of photoresist main material (Adv. Mater. 2008, 20, 3355). At present, the molecular glass developed as a photoresist main material is mainly a branched or cyclic structure compound with photosensitivity (or acid-sensitivity), wherein the branched structure is mainly a rigid structure with multi-benzene ring connection (J. Mater. Chem. 2008, 18, 1903; Chem Mater. 2008, 20, 1606), and the cyclic structure is mainly a calixarene or calixarene-like structure (J. Mater. Chem. 2008, 18, 3588; J. Mater. Chem. 2010, 20, 4445). In addition to photosensitivity (or acid-sensitivity), the glass transition temperature (Tg) and the film-forming property are two most important indicators to determine whether the molecular glass has applicability, when the molecular glass is designed and synthesized. If the synthetic compound is easy to crystallize or the glass transition temperature (Tg) is lower than 100° C., the glass transition temperature (Tg) and the film-forming property will directly affect the application of the molecular glass as a photoresist main material.
Spirofluorene structure has a geometric skeleton with two planes thereof being perpendicular to each other, which can effectively suppress inter-molecules crystallization and can be easy to form a film, meanwhile the spirofluorene has a good rigid structure, a high glass transition temperature and a good thermal stability. It will contribute to the improvements of the glass transition temperature and the film-forming property to design and synthesize a molecular glass based on the spirofluorene structure.